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In this study, graphene oxide paper is obtained via vacuum‐assisted filtration of graphene oxide solution to prepare self‐standing electrodes for supercapacitors. Simultaneous reduction and N‐doping of graphene oxide paper are performed by chemical reduction followed by thermal annealing. Influence of different reduction techniques on the electrochemical properties of the self‐standing papers is investigated. N‐doped reduced graphene oxide papers are decorated with iron oxide nanoparticles to increase the energy density of the material. Increasing the amount of iron oxide nanoparticles in the composite paper results in enhanced capacitance. In the galvanostatic charge‐discharge measurements, iron oxide/N‐doped reduced graphene oxide electrode exhibits specific capacitance of 203 F g−1 at 0.5 mA cm−2. This value is remarkable since the electrode has a high mass loading of 2 mg cm−2, which shows that the electrode can be used for practical purposes. Moreover, these electrodes operate in a wide potential window (1.6 V) and exhibit 79 % capacitance retention at 10000 cycles. [ABSTRACT FROM AUTHOR]

Abstract Here we describe a screen-printed supercapacitor produced onto filter paper using poly (3, 4-ethylene dioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS)/multiwall carbon nanotube (MWCNT) composite as active materials. We use a gel-like electrolyte based on poly (vinyl alcohol) and phosphoric acid (PVA/H 3 PO 4), serving as both an ionic conductor and as an electrode separator. The electrodes are physically characterized through micro-Raman scattering analyses, sheet resistance measurements as a function of the printed number of layers and through scanning electron microscopy. The supercapacitor performance is investigated through impedance spectroscopy, equivalent circuit fitting, cyclic voltammetry (CV), long-term cycle stability and galvanostatic charge/discharge. The electrodes exhibit a low sheet resistance, reaching 17 Ω sq−1, being suitable for use as both electrode and the current collector. The supercapacitor shows good capability behavior over impedance spectroscopy and CV measurements, and 72% of capacitance retention after 1000 cycles. We find a maximum specific capacitance of 20,3 F g−1 for a charge/discharge current of 1 mA, and equivalent series resistance of 60 Ω, leading to energy and power densities of 3,1 Wh kg−1 and 420 W kg−1, respectively. In conclusion, we describe here a flexible supercapacitor without metal collectors produced by a simple printing method. Highlights • A paper based supercapacitor was prepared using screen-printed electrodes. • Screen-printed PEDOT:PSS/MWCNT on paper exhibited a sheet resistance of 17 Ω sq.−1. • The paper-based supercapacitor exhibited a specific capacitance of 20,3 F g−1. [ABSTRACT FROM AUTHOR]

Abstract With the rapid development of flexible electronics, new opportunities are opening up for paper-based electrodes. Herein, an integrated paper electrode consisting of homogeneously mixed cellulose fibers, activated carbon (AC), and carbon black is fabricated using cotton stalks as the raw material. Assembled from two such electrodes, the flexible supercapacitor exhibits high energy density, high power density, and outstanding cyclability. Remarkably, the thickness and AC mass loading of the paper electrode can be easily scaled up to commercial levels (610 µm and 9.8 mg cm−2), while still delivering great performances. Moreover, it is demonstrated that the replacement of AC with Ni-Co layered double hydroxide or Fe 2 O 3 can result in paper-based asymmetric supercapacitor with extremely high energy density (331 μW h cm−2 and 10.3 mW h cm−3), substantially outperforming conventional paper-based supercapacitors. The fabrication methodology of integrated paper electrodes in this report manifests great potential, offering a new vision for flexible energy storage. Graphical abstract fx1 Highlights • An integrated paper electrode is fabricated using cotton stalks as the raw material. • The paper is composed of homogeneously mixed cellulose fibers, AC, and CB. • The paper thickness and AC mass loading can be easily scaled up to commercial levels. • The flexible symmetric supercapacitor delivers favorable energy and power densities. • The paper-based asymmetric supercapacitor exhibits extremely high energy density. [ABSTRACT FROM AUTHOR]

Flexible paper electrodes for supercapacitors were prepared with partially-exfoliated graphite and polypyrrole as the active materials. Graphite was coated on paper with pencil drawing and then electrochemically exfoliated using the cyclic voltammetry (CV) technique to obtain the exfoliated graphite (EG)-coated paper (EG-paper). Polypyrrole (PPy) doped with β-naphthalene sulfonate anions was deposited on EG-paper through in-situ polymerization, leading to the formation of PPy-EG-paper. The as-prepared PPy-EG-paper showed a high electrical conductivity of 10.0 S·cm-1 and could be directly used as supercapacitor electrodes. The PPy-EG-paper electrodes gave a remarkably larger specific capacitance of 2148 F·g-1 at a current density of 0.8 mA.cm-2, compared to PPy-graphite-paper (848 F·g-1). The capacitance value of PPy-EG-paper could be preserved by 80.4% after 1000 charge/discharge cycles. In addition, the PPy-EG-paper electrodes demonstrated a good rate capability and a high energy density of 110.3 Wh·kg-1 at a power density of 121.9W·kg-1. This work will pave the way for the discovery of efficient paper-based electrode materials. [ABSTRACT FROM AUTHOR]

A simple and scalable direct laser machining process to fabricate MXene-on-paper coplanar microsupercapacitors is reported. Commercially available printing paper is employed as a platform in order to coat either hydrofluoric acid-etched or clay-like 2D Ti3C2 MXene sheets, followed by laser machining to fabricate thick-film MXene coplanar electrodes over a large area. The size, morphology, and conductivity of the 2D MXene sheets are found to strongly affect the electrochemical performance due to the efficiency of the ion-electron kinetics within the layered MXene sheets. The areal performance metrics of Ti3C2 MXene-on-paper microsupercapacitors show very competitive power-energy densities, comparable to the reported state-of-the-art paper-based microsupercapacitors. Various device architectures are fabricated using the MXene-on-paper electrodes and successfully demonstrated as a micropower source for light emitting diodes. The MXene-on-paper electrodes show promise for flexible on-paper energy storage devices. [ABSTRACT FROM AUTHOR]

A simple, facile and low-cost method for recycling of supercapacitor materials is proposed. This process aims to recover some fundamental components of a used supercapacitor, namely the electrolyte salt tetraethyl ammonium tetrafluoroborate (TEABF4) dissolved in an aprotic organic solvent such as acetonitrile (ACN), the carbonaceous material (activated charcoal, carbon nanotubes) purified, the current collector (aluminium foil) and the separator (paper) for further utilization. The method includes mechanical shredding of the supercapacitor in order to reduce its size, and separation of aluminium foil and paper from the carbonaceous resources containing TEABF4 by sieving. The extraction of TEABF4 from the carbonaceous material was based on its solubility in water and subsequent separation through filtering and distillation. A cyclic voltammetry curve of the recycled carbonaceous material revealed supercapacitor behaviour allowing a potential reutilization. Furthermore, as BF4− stemming from TEABF4 can be slowly hydrolysed in an aqueous environment, thus releasing F− anions, which are hazardous, we went on to their gradual trapping with calcium acetate and conversion to non-hazardous CaF2. [ABSTRACT FROM AUTHOR]

A solid-state powerful supercapacitor (SC) is fabricated with a substrate of Xerox paper. Its current collector based on a foldable electronic circuit is developed by simply pencil drawing. Thin graphite sheets on paper provide effective channels for electron transmission with a low resistance of 95 Ω sq. The conductive organic material of polypyrrole coated on thin graphite sheets acts as the electrode material of the device. The as-fabricated SC exhibits a high specific capacitance of 52.9 F cm at a scan rate of 1 mV s. An energy storage unit fabricated by three full-charged series SCs can drive a commercial light-emitting diode robustly. This work demonstrated a simple, versatile and cost-effective method for paper-based devices. [ABSTRACT FROM AUTHOR]

Graphene and porous carbon materials are widely used as electrodes in supercapacitors. In order to form mechanically stable electrodes, binders can be added to the conducting electrode material. However, most binders degrade the electrical performance of the electrodes. Here we show that by using nanofibrillated cellulose (NFC) as a binder the electrical properties, such as capacitance, were enhanced. The highest capacitance was measured at an NFC content of approximately 10 % in ratio to the total amount of active material. The NFC improved the ion transport in the electrodes. Thus, electrodes made of a mixture of nanographite and NFC achieved larger capacitances in supercapacitors than electrodes with nanographite only. In addition to electrical properties, NFC enhanced the mechanical stability and wet strength of the electrodes significantly. Furthermore, NFC stabilized the aqueous nanographite dispersions, which improved the processability. Galvanostatic cycling was performed and an initial transient behaviour of the supercapacitors during the first cycles was observed. However, stabilized supercapacitors showed efficiencies of 98-100%. [ABSTRACT FROM AUTHOR]

Paper, in addition to its frequent usage in writing, packaging, printing, etc., has gained comprehensive utility as a flexible and conductive base in sensors, solar energy harvesting, conversion, and storage applications. This is due to its strategic-aiding aspect in terms of environmental friendliness, cost-effectiveness, recyclability, thin, flexible and lightweight nature, biocompatibility, etc., required to develop next-generation flexible devices. The signs of progress in paper-based devices are seen in matured technologies of the paper-based sensor for varied sectors. Also, there have been wide-ranging research efforts on developing paper-based high-performance energy harvesting, conversion, and storage solutions. However, it is a newly emerging area and needs a fundamental and state-of-the-art understanding for future devices development. Thus, the current review summarizes the research progress in this field utilizing paper, understanding fundamental properties w.r.t application, performance enhancement w.r.t material advancements (i.e. paper modification), and technological trends, which is otherwise not yet reviewed earlier. It further sheds light upon the perspectives for their associated and allied technological developments in the energy sector. [Display omitted] • Role of paper properties in energy related applications are discussed. • Paper based electrodes for energy harvesting and conversion devices. • Utilty of papers in energy storage i.e. supercapacitors and batteries is presented. • Challenges and perspectives of realization of paper based devices for energy sector are projected. [ABSTRACT FROM AUTHOR]

Recently our modern society is demanding flexible, low-cost, and lightweight electrochemical energy storage systems, which are very important in variety of applications ranging from portable consumer electronics to large industrial-scale power and energy management. Among different energy storage systems, flexible supercapacitors have been considered as one of the most promising candidates due to their significant merits such as high power density along with the unique properties of being flexible, lightweight, shape versatile, and eco-friendly in comparison to other energy storage systems. In this regard, this review article describes the principles of supercapacitors and the recent research progress on flexible supercapacitor electrodes, for which metal substrates, carbon-based paper, conventional paper, textiles, sponges, and cables are used as substrates to fabricate high-performance flexible supercapacitors. Finally, the future challenges and perspectives for the development of flexible supercapacitors based on bendable substrates and their applications are discussed. [ABSTRACT FROM AUTHOR]

Paper, invented more than 2,000 years ago and widely used today in our everyday lives, is explored in this study as a platform for energy-storage devices by integration with 1D nanomaterials. Here, we show that commercially available paper can be made highly conductive with a sheet resistance as low as 1 ohm per square (π/sq) by using simple solution processes to achieve conformal coating of single-walled carbon nanotube (CNT) and silver nanowire films. Compared with plastics, paper substrates can dramatically improve film adhesion, greatly simplify the coating process, and significantly lower the cost. Supercapacitors based on CNT-conductive paper show excellent performance. When only CNT mass is considered, a specific capacitance of 200 F/g, a specific energy of 30-47 Watt-hour/kilogram (Wh/kg). a specific power of 200,000 W/kg, and a stable cycling life over 40,000 cycles are achieved. These values are much better than those of devices on other flat substrates, such as plastics. Even in a case in which the weight of all of the dead components is considered, a specific energy of 7.5 Wh/kg is achieved. In addition, this conductive paper can be used as an excellent lightweight current collector in lithium-ion batteries to replace the existing metallic counterparts. This work suggests that our conductive paper can be a highly scalable and low-cost solution for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Flexible supercapacitor with all components monolithically integrated into an on-chip paper substrate demonstrates excellent electrochemical and mechanical performance. Supercapacitors are drawn with a conductive ink of nitrogen-doped carbon nanotube and graphene ink, which has been prepared without assistance of surfactant. The engineering strategy is intrinsically scalable toward flexible paper devices. [Display omitted] • A surfactant-free ink of nitrogen-doped carbon nanotubes and graphene is prepared. • The electrodes are integrated onto a paper in mirror image. • The resultant supercapacitor presents a high volumetric capacitance of 0.45 F cm−3. • The strategy is intrinsically scalable toward flexible supercapacitors. We demonstrate a facile strategy to fabricate flexible paper-based supercapacitors, in which all the components are integrated onto a paper with poly (vinyl alcohol)/H 3 PO 4 as the gel electrolyte. The electrodes are drawn on both sides of the paper in a mirror image with a surfactant-free ink of nitrogen-doped carbon nanotubes and graphene. The resultant supercapacitors present a high volumetric capacitance of 0.45 F cm−3 and an energy density of 40.0 μWh cm−3. Moreover, this strategy is intrinsically scalable toward flexible energy devices while maintaining their electrochemical and mechanical performance. [ABSTRACT FROM AUTHOR]

Here, we prepared planar polypyrrole (PPy) coated paper-based supercapacitors by applying simple laser carving assisted method. The planar structure of the device showed a significant performance improvement (13.9 mF/cm2) compared to the sandwiched structure device (12.3 mF/cm2). In addition, by adjusting the polymerization time of pyrrole, the device capacity can be further increased to 87.4 mF/cm2. We firmly believed that the laser carving assisted method has a significant role in promoting the development of flexible planar electronic devices. • Planar PPy coated paper-based supercapacitors were obtained by laser carving. • The planar device showed a significant performance improvement. • The optimal device capacity can be further increased to 87.4 mF/cm2. Paper-based supercapacitors have attracted more and more attention for high electrochemical performance. However, most of them adopt sandwiched structure. Here, we prepared planar polypyrrole (PPy) coated paper-based supercapacitors by applying simple laser carving assisted method. The planar device showed a significant performance improvement (13.9 mF/cm2) compared to the sandwiched device (12.3 mF/cm2). In addition, by adjusting the polymerization time of pyrrole, the device capacity can be further increased to 87.4 mF/cm2. We firmly believed that the laser carving assisted method has a significant role in promoting the development of flexible planar electronic devices. [ABSTRACT FROM AUTHOR]

Flexible Supercapacitors: The Inside Cover picture illustrates flexible supercapacitors made with several different substrate types for which flexibility and mechanical stability are of the utmost importance. These devices can provide electrical energy to flexible, wearable, and lightweight electronics for portable applications. In the Review by Won Bae Kim, Rudolf Holze, and co‐workers at Gwangju Institute of Science and Technology and Technische Universität Chemnitz on page 325, the authors review the basic principles of flexible supercapacitors and the latest research advances that are moving this field forward. In particular, recent progress on flexible supercapacitor electrodes is reviewed with respect to bendable substrates, and their properties are discussed in detail. [ABSTRACT FROM AUTHOR]